Known TDD's are used by operators to communicate with the deaf via standard telephone lines. Such known operator TDDs typically include a limited keyboard for sending TDD messages, a display for displaying incoming and outgoing messages and a printer that provides a hard copy record of TDD communications. The keyboards used for known TDDs are small, having closely spaced keys which make these devices difficult to use. Further known TDDs typically are not directly coupled to a telephone line. More particularly, these known TDDs use an acoustic coupler in which the handset of a telephone is placed, the coupler transmitting by sound the tones from the telephone handset to the TDD. Couplers, however cannot be used with telephone headsets. Further, if the shape of the acoustic coupler's rubber cup does not conform to the shape of the handset placed in the cup, data can be lost. Other expensive TDDs are known that are connected directly to the telephone line at the line's tip and ring connection. This connection can cause problems, however, when installed at a public safety answering point, PSAP, utilizing multiple telephone lines. At PSAP's the TDD operator typically uses a computer also. However, a fairly large work space is required to accommodate the TDD, the computer and the computer keyboard.
TDD products are also known that are resident in a computer requiring resident software. However, software compatibility problems can arise with other software application programs run on the computer.